The mechanism of action of epidermal growth factor (EGF) on liver cells and fibroblasts cell lines will be investigated in conjunction with experiments to elucidate the function of this polypeptide hormone in the overall growth and development of the organism. Since EGF has been shown to act in combination with insulin and glucagon to stimulate hepatic proliferation in intact adult animals, it is planned to investigate the nature of this synergism and its role in the regulation of cell growth and differentiation. Several parameters will be evaluated to assess the biological responses which occur following binding of EGF to the cell. The rates of synthesis of RNA, DNA, and protein will be measured as well as the activities of certain key enzymes intimately associated with DNA synthesis. The mechanism of action and biological effects of EGF on liver, will be studied using a homogeneous population of adult rat liver parenchymal cells maintained as non-dividing primary cultures will be used as a model system. We have determined that 125I-labeled EGF is capable of binding to these cultured hepatocytes in a specific and saturable manner and that it is capable of entering the hepatocyte and being metabolized. Recently developed culture conditions have more than doubled the functional lifespan of the hepatocytes in primary culture which will permit an assessment of the short and long term effects of EGF on the liver parenchymal cell. A broad spectrum of monoclonal antibodies directed towards different antigenic sites on the EGF molecule will be developed to study the structural region of the molecule which is involved in the specific binding of EGF to its cellular receptor. Monoclonal antibodies to the EGF receptor will also be produced and used as probes to investigate the early cellular events associated with the mitogenic properties of EGF.